This invention relates generally to electrolytic halogenators for use in the production of halogen biocidally active agents for the disinfection and sanitizing of waters. More particularly, the present invention relates to an improved monopolar electrolytic cell that is used in conjunction with a circulating pump associated with the circulation of water in a swimming pool to generate a dilute quantity of sodium hypochlorite solution from water containing dilute quantities of salt.
Chlorine has long been used as a biocidally active agent for use in water in swimming pools or cooling towers, in addition to drinking water. This has traditionally been accomplished with the chemical treatment of these waters with chemical compounds, such as granular or tabletted hypochlorite compounds. Several disadvantages result from the use of chemical compounds to accomplish this. These include the necessity to retain water treatment chemicals on site and the fluctuation in the water quality level due to the periodic additions to the water of the pool chemicals by either broadcast or floating dissolution methods.
More recently electrolytic chlorinators have been used to produce dilute quantities of sodium hypochlorite solutions from waters containing dilute quantities of salt. Two general types of electrolytic chlorinators are in use. The first type employs the monopolar electrode system with at least two platinum electrodes that are expanded mesh, conical in shape, and concentrically arranged within the cell. This type of design has limitations. The salt concentrations must be kept relatively high because of the low chlorine activity of the electrodes. Salt concentrations of approximately 6,000 parts per million must be used. The active electrode area within the cell of this design is reduced because of the expanded mesh design employed. Additional electrodes cannot be easily added because of the conical shape and the concentrical arrangement within the electrolytic cell.
The second type of electrolytic chlorinator employs a bipolar electrode arrangement with approximately 15 flat plate electrodes. The electrode spacing in this design is very narrow in order to control the cell voltage requirements. This narrow spacing increases the possibility of hardness scale building up on the electrodes and the possibility of electrical short circuiting occuring. A bipolar electrode configuration requires relatively high voltage which can produce leakage currents that are corrosive to other components in the system. To counteract this corrosion problem, sacrificial target electrodes are required to be used.
These problems are solved in the design of the electrolytic halogenator of the present invention by employing plate electrodes with a unique shape and a constant spacing and planarity to maintain low voltage performance by the halogenator with even current distribution across the electrodes.